Thank you for clearing that out...That means the fuckers in grow shop are trying to sell used bulbs...dam !!! I would have never thought that of them...what a is going on in this world...jaw dropping
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Hi dude, dont be sad.
The fresh new bulb could be like this, the factory do ignition test before ship them out. The ignition test is like its name, to see if this bulb can be light up or not. It is a standard QC control.
Why this one dark the two sides of arc tube?
Because when ignition test, they light it up for few seconds and take it off right after, in this very short time the bulb has not reached the working temp, mercury compound inside was gasified and solidificate in few sec, mercury will stick on "cold" arc tube to perform like what is on your pic.
Is this black end means bad bulb?
No, as what i mentioned, it caused by QC test. To light it up again, and the black would be gone in 5 mins.
Why in the same brand, some new purchased products have this, some dont?
Because this factory done sampling QC test. The one been test appeared black.
Why some brands have not got this issue at all?
Because the factory of this brand, done few mins aging to disppear the black caused by QC test.
However, in some case if the black still be there on a new purchase bulb after you light it up for mins. This bulb might be disqualified.
The black ends on a qualified bulb normally appear after very long time usage, and the black color comes from the electrode not the mercury, and it means the bulb reachs its end life.
Hope this can sort things out for you.